A dual-channel photonic crystal filter model (AB)m(LC)H(LC)(BA)m was proposed with nematic liquid crystal as defect layer. Modulation characteristics of external electric field to the filter were studied by method of combining transmission matrix with electro-optic effect of nematic liquid crystal. The results show that the linear relationship between the central frequency of the double filter channel shows that the modulation effect of the voltage on the filter frequency is very good. The response sensitivity of the two channel filter bandwidth to the external field voltage is different, and the bandwidth of long wave channel is more sensitive to the voltage than the other one. When the voltage is small enough, the modulation range of the voltage to the filter bandwidth is large, and the modulation law is obvious.The filter bandwidth can be adjusted by selecting the appropriate voltage range. These characteristics provide definite reference to design of new optical filter.